Technical Field
The present invention relates to compositions for making contacts, contacts made therewith, and methods for making contacts. More specifically, the present invention relates to: a composition for making a contact which composition contains a predetermined amount of cobalt and a predetermined amount of sulfur and has a predetermined average particle size, thereby making it possible to achieve a short-stroke contact that exhibits a high Young's modulus; a contact made therewith; and a method for making a contact.
Related Art
Connectors are widely used to attach and detach an electronic part, a cable, or the like to and from another part for mutual exchange of electrical power, a signal, or the like between the parts or between the part and the cable. A connector includes: a housing constituted by an insulator such as resin; and a contact constituted by metal.
Such a contact needs to be pressed against a conductive member of a part to which it is connected, such as an electrode of a battery, so as to be in touch (sliding contact) with the conductive member. In order to maintain the touch, the contact is required to elastically deform in resistance to a load being applied to the contact along with the touch and, when the load has been removed, elastically deform to return to the state in which it had been before the application of the load.
FIG. 5 is a vertical cross-sectional view showing an example of a contact of a common battery connector. (a) of FIG. 5 shows a state in which no load is being applied, and (b) of FIG. 5 shows a state in which a load is being applied.
In FIG. 5, a contact 200 includes: a retaining section 201, which is fixed by an insulator; a contact section 202, which makes sliding contact with a conductive member; and an elastic deformation section 203, which connects the retaining section and the contact section to each other and which is elastically deformable. The contact 200 is connected to a conductive member 204.
Sliding contact of the contact section 202 with the conductive member 204 causes a load to be applied to the elastic deformation section 203, with the result that, as shown in (b) of FIG. 5, the elastic deformation section 203 elastically deforms. The larger the amount of displacement of the elastic deformation section 203 along with the application of the load is, i.e., the longer the stroke is, the larger the force of contact between the contact 200 and the conductive member 204 is.
In recent years, there has been an expansion in battery capacity of multifunctional portable phones (smartphones) that use a variety of applications, and there has been an increase in battery size accordingly. However, as opposed to such an expansion in battery size, there has been a demand for a reduction in size of portable phones. Therefore, there has been a demand for reductions in height and size of connectors that connect batteries and substrates.
As mentioned above, the longer the stroke is, the larger the force of contact between the contact and a conductive member is. However, for a reduction in height of the connector, it is necessary to ensure contact force with the stroke made shorter. In this specification, the stroke for achieving necessary and sufficient contact force required of the contact is referred to as “short stroke”.
For a short stroke, i.e. for necessary and sufficient contact force with a small stroke, it is necessary for the contact to be constituted by a material having a high Young's modulus.
Repetition of attachment and detachment of a contact causes the stress of a load to go beyond the acceptable range of stress, with the result that the contact is damaged by fatigue. Therefore, it is necessary to limit the stress of a load to the acceptable range of stress or lower. In order for the stress of a load to fall within the acceptable range of stress, it is necessary for the material constituting the contact to have a high 0.2% proof stress.
Further, since the contact is used in applications where it is necessary to pass an electric current through the contact, a high conductivity is required. A low conductivity results in generation of heat due to power loss, thus making it impossible to pass an electric current. Further, from a point of view of energy conservation, a reduction in power loss is required.
Further, since the contact becomes lower in conductivity by rusting over time, the contact is required to have a certain degree of corrosion resistance.
There is a phenomenon known as “copper damage”, in which a metal such as copper or cobalt degrades a resin such as polyimide by reacting with the resin. Since the retaining section of a contact is usually composed mainly of resin, an occurrence of copper damage invites damage to the retaining section, thus making it impossible to achieve necessary and sufficient contact force.
Therefore, a contact that can cause copper damage to occur imposes a limitation on the types of resin that can be used, and as such, cannot be extended to versatile applications.
Patent Literature 1 discloses a contact formed into a spiral shape by using an electroformed layer made of a copper-tin (Cu—Sn) alloy having a tin composition ratio of 5 at % or greater to 25 at % or less. The contact disclosed in Patent Literature 1 has its tin composition ratio adjusted so that a high 0.2% proof stress and a high conductivity can be achieved.
However, as will be confirmed below in Comparative Example 7 by the inventors of the present invention, the copper-tin alloy has a low Young's modulus. Therefore, the contact disclosed in Patent Literature 1 is thought to be in a spiral shape with a large stroke for the purpose of achieving necessary and sufficient contact force.
Further, Patent Literature 2 discloses an elastic contact maker formed by using an electroformed layer made of a nickel-cobalt (NiCo) alloy having its cobalt composition ratio adjusted to 1 at % or greater to 30 at % or less and having its average particle size adjusted to 20 nm or smaller.
The contact maker disclosed in Patent Literature 2 has both its cobalt composition ratio and its particle size adjusted so that a high 0.2% proof stress (yield stress) can be achieved.
However, the contact maker disclosed in Patent Literature 2 must have an average particle size adjusted to 20 nm or smaller. As will be confirmed below in Comparative Example 5 by the inventors of the present invention that the conductivity of a composition for making a contact which composition has an average particle size of 60 nm is low, the conductivity of the elastic contact maker is thought to be similarly low.
Therefore, the elastic contact maker disclosed in Patent Literature 2 is thought to be limited exclusively to a special application, as in the case of semiconductor inspection equipment, in which a high conductivity is not required.